In Evolved Universal Terrestrial Radio Access (E-UTRA) specified in 3GPP, an acknowledgement (ACK) signal or a negative acknowledgement (NACK) signal and a channel quality information (CQI) signal, which are control information, are transmitted by use of a physical uplink control channel (PUCCH). In the following description, an ACK signal and a NACK signal are both referred to as A/N signal in short for convenience.
When cyclic prefix (CP) is normal mode and PUCCH is format 2, only CQI signals are multiplexed. In contrast, when CP is normal mode and PUCCH is format 2a or format 2b, a CQI signal and an A/N signal are multiplexed in a same subframe (refer to Chapter 5.4.2 of NPL 1).
As illustrated in FIG. 1, an A/N signal is multiplexed into an OFDM symbol that is assigned to a reference signal in the latter half (=OFDM symbol number #5) of a slot. Here, the OFDM denotes orthogonal frequency division multiplexing. In the following description, a reference signal for demodulation is referred to as DM-RS (i.e., demodulation reference signal).
As illustrated in FIG. 1, upon receipt of a radio signal in which a DM-RS and an A/N signal are multiplexed, a receiver detects the A/N signal, which is multiplexed with a reference signal, carries out CQI channel estimation by use of the reference signal from which the A/N signal is removed, and uses estimated channel characteristics for demodulation of CQI signals. In order to reduce the influence of false detection of an A/N signal in such A/N detection, a wireless base station has been suggested (PTL 1). The wireless base station includes A/N detection units that have different criteria for detection upon which to determine whether the A/N signal is ACK or NACK, and equalizes the received DM-RSs in the first half and the latter half (OFDM symbol numbers #1 and #5) of the slot, so that noise is reduced.